How does my MacBook power up?

How does my MacBook power up? (For end users)

1. Once you connect MagSafe to the Mac, the System Management Controller (SMC) will talk to the chip on the MagSafe and the green light turns on.

2. The charging circuit receives power from Magsafe and starts charging the battery if it is not fully charged and the orange light turns on.

3. Once you press power button and this action is detected by SMC, several different power rails will be created.

4. The memory module (RAM) receives power first, followed by the CPU, hard drive, DVD drive, and graphics chip.

5. SMC will check all the power rails. If everything is fine, SMC will send a “reset” signal to the CPU.

6. Upon received the reset signal, the CPU will read and execute the BIOS/EFI codes, performing a Power-On-Self-Test (POST). The BIOS/EFI is a collection of hardware specific codes stored in a read-only chip. All Mac model has its own unique BIOS/EFI. OSX talks to BIOS/EFI and BIOS/EFI talks to the specific hardware in turn, so OSX can be run on different MacBook models.

7. Mac will chime and the Apple logo will be displayed. Apple’s OSX software will then commence loading.

8. Enjoy using your Mac and stay away from the Mac’s arch-enemy: your DRINK

How does my MacBook power up? (For power users)

1. Once you connect MagSafe to the Mac, the System Management Controller (SMC) will read code from the chip on the MagSafe connector to identify the specific charger type it is connected to. The charger outputs a preset voltage (14.5/16.5/18.5/20) with a 1 second delay, after the connection is stabilized and charger type identified. The green light then turns on.

2. The charging circuit will receives power from MagSafe. SMC reads the chip on the battery to get the battery status to determine charging current. If battery is empty then high current will be applied (fast charging mode).The current will be gradually reduced when battery is near full. The orange light turns on while the battery is being charged. Once the battery is full charged the green light will turn on again and no more current will be sent to the battery. It is safe to connect MagSafe all the time while you are working on your Mac as it will not overcharge and therefore damage a fully charged battery. In fact, some GPUs will not run at full power until a charger is connected.

3. Once you press the power button and this action is detected by SMC, SMC will pass the message to the Platform Controller Hub (PCH). PCH will switch on power management chips to create several different voltage power rails for different devices. More than 50% of faulty logic boards are related to one or more missing or unstable power rails .

4. The memory module (RAM) will receive the power first followed by the CPU, hard drive, DVD drive, graphics chip, screen, sound card, and WiFi card.

5. All power rails report to SMC by sending PG (power good) signals. The SMC will shut down all power rails if any of them fails to send a PG signal. A large number of voltage and current sensing circuits in addition to other protective circuits are implemented in the MacBook logic board as safety measures. As a result, a lot more components (IC, transistor, resistor, capacitor, and inductor) are used on the Macbook logic board than other brand names of laptop. If everything is OK, SMC will send a “reset” signal to the CPU.

6. Upon receiving a reset signal, the CPU will load BIOS/EFI codes (Hardware specific codes stored in the ROM chip) to the memory module and execute the Power-On-Self-Test (POST) codes. After POST, all devices including the hard drive, optical drive, USB, sound, WiFi, and GPU will be initialized and ready to go.

7. The Mac will chime and activate the screen back-light. The CPU then executes the BIOS/EFI input/output codes to access bootable devices such as a hard drive, and searches for operating system loader. If no hard drive is found or the hard drive does not have a loader, a question mark will be displayed. If a loader is found, the Apple logo will be displayed. The CPU then executes the loader and loads the rest of Apple’s OSX software on your Mac. You will see a loading progress bar while OSX being loaded (older OSX versions show a rotating gear).

8. The loader loads the core OSX first followed by application and hardware drivers. MacBooks with graphics issues usually start going wrong at 2/3rds of the loading progress bar, which corresponds to the moment the graphics driver is being loaded and executed.

9. Upon finishing loading, control is passed to OSX and OSX then passes control to you. Now you can control the machine by keyboard, mouse, and voice commands (on macOS Sierra or newer). You are now free to use your Mac while keeping it away from it’s worst enemy: your DRINK

If even greater detail, please proceed to the advanced article “How does a MacBook power up? (For computer technicians).

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